1. Field of the Invention
The present invention relates to photographic processes and products wherein certain light-absorbing dyes are employed as optical filter agents to protect a selectively exposed photosensitive material from further exposure by incident radiation actinic thereto during processing in the presence of light and to novel indole phthaleins useful therein.
2. DESCRIPTION OF THE PRIOR ART
The production of both silver and color images including monochromatic and multicolor images employing diffusion transfer techniques is now well-known. In these processes, a photosensitive element comprising a layer of photosensitive material is exposed to provide a latent image therein and wetted by a liquid processing composition, for example, by immersion, coating, spraying, flowing, etc., in the dark, and the exposed photosensitive element superposed prior to, during or after wetting, on a sheetlike support element which may be utilized as an image-receiving element. As a function of developing the latent image, there is formed an imagewise distribution of image-forming components which imagewise distribution is transferred, by imbibition, to form the final image either in the photosensitive or image-receiving element.
U.S. Pat. No. 3,415,644, discloses a composite photosensitive structure, particularly adapted for use in reflection type photographic diffusion transfer color processes. This structure comprises a plurality of essential layers including, in sequence, a dimensionally stable opaque layer; one or more silver halide emulsion layers having associated therewith dye image-providing material which is soluble and diffusible, in alkali, at a first pH, as a function of the point-to-point degree of its associated silver halide emulsion's exposure to incident actinic radiation; a polymeric layer adapted to receive solubilized dye image-providing material diffusing thereto; a polymeric layer containing sufficient acidifying capacity to effect reduction of a processing composition from the first pH to a second pH at which the dye image-providing material is substantially nondiffusible; and a dimensionally stable transparent layer. This structure may be exposed to incident actinic radiation and processed by interposing, intermediate the silver halide emulsion layer and the reception layer, an alkaline processing composition providing the first pH and containing a light-reflecting agent, for example, titanium dioxide to provide a white background. The light-reflecting agent (referred to in said patent as an "opacifying agent") also performs an opacifying function, i.e., it is effective to mask the developed silver halide emulsions and also acts to protect the photoexposed emulsions from postexposure fogging by light passing through the transparent layer if the photoexposed film unit is removed from the camera before image formation is complete.
In a preferred embodiment, the composite photosensitive structure includes a rupturable container, retaining the alkaline processing composition having the first pH and reflecting agent, fixedly positioned extending transverse a leading edge of the composite structure in order to effect, upon application of compressive pressure to the container, discharge of the processing composition intermediate the opposed surfaces of the reception layer and the next adjacent silver halide emulsion.
The liquid processing composition distributed intermediate the reception layer and the silver halide emulsion, permeates the silver halide emulsion layers of the composite photosensitive structure to initiate development of the latent images contained therein resultant from photoexposure. As a consequence of the development of the latent images, dye image-providing material associated with each of the respective silver halide emulsion layers is individually immobilized as a function of the point-to-point degree of the respective silver halide emulsion layer photoexposure, resulting in imagewise distributions of mobile dye image-providing materials adapted to transfer, by diffusion, to the reception layer to provide the desired transfer dye image. Subsequent to substantial dye image formation in the reception layer, a sufficient portion of the ions of the alkaline processing composition transfers, by diffusion, to the polymeric neutralizing layer to effect reduction in the alkalinity of the composite film unit to the second pH at which dye image-providing material is substantially non-diffusible, and further dye image-providing material transfer is thereby substantially obviated.
The transfer dye image is viewed, as a reflection image, through the dimensionally stable transparent layer against the background provided by the reflecting agent, distributed as a component of the processing composition, intermediate the reception layer and next adjacent silver halide emulsion layer. The thus-formed stratum effectively masks residual dye image-providing material retained in association with the developed silver halide emulsion layer subsequent to processing.
In the copending U.S. Patent application Ser. No. 786,352 of Edwin H. Land, filed Dec. 23, 1968, now abandoned, and copending U.S. Patent application Ser. No. 101,968 filed Dec. 28, 1970, now U.S. Pat. No. 3,647,437; in part a continuation of Ser. No. 786,352, an organic light-absorbing reagent (or optical filter agent), such as a dye, which is present as a light-absorbing species at the first pH and which may be converted to a substantially non-light-absorbing species at the second pH is used in conjunction with the light-reflecting agent to protect the selectively exposed silver halide emulsions from post-exposure fogging when development of the photoexposed emulsions is conducted in the presence of extraneous incident actinic radiation impinging on the transparent layer of the film unit.
In the copending U.S. Patent application Ser. No. 43,782, of Edwin H. Land, filed June 5, 1970, now abandoned, the stratum interposed intermediate, the reception layer and next adjacent silver halide layer is disclosed to comprise an inorganic light-reflecting pigment dispersion containing reflecting pigment in a concentration per se insufficient, distributed as a layer intermediate the reception layer and next adjacent silver halide layer, to effectively prevent transmission of a given level of radiation actinic to the silver halide layer therethrough and at least one optical filter agent at a pH above the pKa of the optical filter agent, in a concentration per se also insufficient to prevent transmission of said given level of actinic radiation therethrough, which concentrations individually and additively are together insufficient to prevent said transmission of incident actinic radiation but in admixture are synergistically effective to provide the requisite transmission density to prevent such transmission of said given level of radiation until modulation of the environmental pH to below the pKa of the optical filter agent whereby the transmission density is rendered sufficiently low to permit substantially immediate viewing of transfer image formation against the background provided by the reflecting pigment.